1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a method for forming iridium oxide nanotubes.
2. Description of the Related Art
Recently, the fabrication of nanowires has been explored, due to its potential importance as a building block in nano, microelectromechanical (MEM), and nanoelectromechanical NEM device applications. For example, researchers associated with Charles Lieber have reported the synthesis of a variety of semiconductor nanowires made from materials such as silicon (Si), Si-germanium (SiGe), InP, and GaN, for use in building nano-computing system. Other groups also report using template structures to grow metallic nanowires made of materials such as Ni, NiSi, Au, and Pt. Metallic nanowires can be used for electrical interconnections and the relatively sharps tips of the nanowires make them effective for field emission purposes. ZnO2 nanowires are potentially useful as a light emission element.
However, no processes have been reported that are able to create metallic nanowires without the use of a porous material or template. The templates add a considerable degree of complexity to the process. Thus, a more practical and commercially feasible means of forming metallic nanowires is desirable. It would be especially useful if iridium oxide (IrO2) nanowire could be grown using a metalorganic chemical vapor deposition (MOCVD) methods without a template. IrO2 is a conductive metal oxide that is already widely used in DRAM and FeRAM applications, so its use could be easily integrated into convention IC fabrication. IrO2 can be used as a conductive electrode, as it has stable electrical and chemical properties, even at high temperature O2 ambient conditions. IrO2 can also be used as pH sensor material. Ir thin film can be deposited using PVD easily with excellent polycrystalline structure and strong (111) orientation. IrO2 can be formed afterwards, by oxidizing the Ir film, or it can be formed directly using reactive sputtering method at higher temperatures in oxygen ambient. CVD methods have recently been developed grow Ir and IrO2 thin films. It is relatively easy to maintain good composition control in CVD processes, and the method is know to provide good step coverage.
Reui-San Chen et al. have published a paper that discusses making IrO2 nanorods by MOCVD deposition, using a (methylcyclopentadienyl) (1,5-cyclooctadiene) iridium (I) precursor. They also explored the potential use of IrO2 nanorods in field emission applications. The nanorods they grew were a few microns long, and about 100 nanometers (nm) in diameter. However, successfully repeated experiments obtaining similar vertically aligned IrO2 nanorods show that, although these structures exhibit sharp tips, the crystal structure is amorphous or polycrystalline. The crystalline structure is a result of defects, or a high dislocation density, resulting from the fact that there is insufficient diffusion to overcome the effects of shadowing during growth, which acts to provide more precursor to the nanorod tips than to the nanorod stem, or rod bottom sections.
It would be advantageous if iridium oxide nanorods could be grown in a cluster, to form a hollow nanotube structure, in an MOCVD process.
It would be advantageous if the hollow nanotube could be formed without the use of a template.